FIG. 1A shows an example of a network comprising a first cell (cell A) and a second cell (cell B), having a cell coverage boundary 10. If it is assumed that at least one of the first and second cells comprise multiple distributed transmission points (TPs), and that the cells are deployed close to each other, for example in the same floor of one building, then user equipments (UEs) close to the cell coverage boundary 10 may suffer strong inter cell interference (ICI). In this example cell A has two transmission points labeled A1 and A2, and cell B has two transmission points labeled B1 and B2. In such a scenario UE1 connected to cell A may suffer strong inter cell interference from transmission point B2, while UE2 connected to cell B may suffer strong inter cell interference from transmission point A2.
To help mitigate inter cell interference for cell-edge UEs, standardized inter cell interference coordination techniques can be used. For example, the serving cell A of a victim UE, e.g. UE1, can send a backhaul message to the aggressor cell B, requesting that cell B reduces its transmission power during certain subframes, so that inter cell interference from cell B to UE1 will be reduced, at least in those subframes. Cell B will then reduce the power of its transmission points B1 and B2 in certain subframes (known as reduced power subframes, RPSF), and send a RPSF pattern back to cell A, for example over an X2 backhaul interface. For example, both attenuators gB1 and gB2 in FIG. 1A can be set to −6 dB in some subframes to reduce power in those subframes. Cell A will then configure two channel state information (CSI) measurements for all the UEs in cell A, reflecting protected and non-protected subframes.
It is noted that cell A has no information about which UEs in cell A are strongly interfered by cell B and which are less interfered (since the UE positions in cell A are unknown).
FIG. 1B shows an example of another scenario whereby cell B is more loaded than cell A, and load balancing between the two cells is needed. Load balancing can be provided, for example, using standardized cell range expansion (CRE) and further enhanced inter-cell interference coordination (FeICIC) techniques. For example, a cell selection offset (CSO) of 6 dB can be applied to UEs in cell A to expand the coverage area of cell A, so that UE2 is connected to cell A instead of cell B. On the other hand, cell B may reduce its transmission power during RPSF, so that inter cell interference from cell B to UE2 will be reduced.
The scenarios described above have the disadvantage of leading to reduced capacity problems, because the aggressor cell will reduce the transmission power of all its transmission points simultaneously (e.g. both gB1 and gB2) in the RPSF subframes, leading to reduced performances of all UEs connected to the aggressor cell in those RPSF subframes.